4 PRACTICAL ORGANIC CHEMISTRY
by heating the substance strongly with magnesium powder and
moistening the cold product with water. Magnesium phosphide
is formed and is decomposed by the water, giving phosphine
which is readily detected by its smell.
Carbon and Hydrogen.—The principle of the method is
that described under qualitative examination^ but the substance
and the products of combustion, viz., carbon dioxide and water,
are weighed. The following app'aratus is required.
1. An Rrlenmeyer or other form of Combustion Furnace.—
The usual length is 80-90'cm. (31-35 in.), and it is provided with
30 to 35 burners. Flat flame burners are undesirable.
2. A Drying Apparatus.—A form of drying apparatus which
is easily fitted together is shown in Fig. 2. It consists of four
large U-tubes arranged side by side
in pairs. The U-tubes are mounted
upon a wooden stand with two up-
rights, to which the two pairs of tubes
are wired. The first of each pair is
filled with soda-lime, and the second
with pumice soaked in concentrated
sulphuric acid. Each soda-lime tube
is connected with a sulphuric acid tube
by well-fitting rubber corks and a bent glass tube. The two
other limbs of the sulphuric acid U-tubes are joined by a three-
way-tap forming a T-piece. The free end of the T-piece is
attached to a small bulb
tube, Fig. 3, containing a
drop of concentrated sul-
phuric acid to mark the
rate at which the bubbles
are B^.bg' through the FIG. 3.
is. connect§$, \with the combustion tube by a short
M/ce of rubber tuning and a short glass tube, which passes
through a rubber cork fixed in the end of the combustion tube.
The rubber ".tubing carries a screw-clip. The open eno*s of